1. Field of the Invention
This invention relates to an image drawing apparatus which converts input data into raster information and outputs an image having gradations.
2. Description of the Related Art
In recent years, in the fields of computer graphics, DTP and so forth, apparatus has been developed to convert input graphic data or code data-into raster information such as a bit map and output it to an outputting apparatus such as a display or a printer which can provide a gradation output or a color output.
When input data are to be converted into bit map information and outputted, an outputting apparatus having a low resolution has a drawback in that the degradation of the picture quality by jaggy is remarkable. In order to cope with the problem, it is a conventional practice to produce an enlarged image obtained by raster conversion, process the enlarged image by filter processing to convert it into an image having gradations to smooth an edge portion and output the image. However, very much processing time is required and a memory of a large capacity is required to produce an enlarged image and process the enlarged image by filter processing. Also a technique wherein a gradation at an edge portion is detected from an inclination of a straight line and outputted has been proposed and is disclosed in Japanese Patent Laid-Open Application No. Heisei 4-15771. The technique, however, has a drawback in that, since image drawing processing proceeds along a straight line, when image drawing is performed for each scanning line, much processing time is still required and image drawing for scanning line is not performed at a high rate.